1. Field of the Invention
This invention relates to a washing process for institutional laundries in which different detergents are introduced into the liquor in the same wash cycle, but at different stages of the washing process.
2. Discussion of Related Art
In institutional laundries, different detergents are often introduced into the liquor in the same wash cycle, but at different stages of the washing process, for example first a detergent containing anionic surfactants and later a detergent containing nonionic surfactants. In recent years, washing processes have been continually improved both from the ecological and from the economic point of view. Reductions have been achieved in the use of energy, detergent, water and time. Significant improvements in this regard were obtained in particular by introduction of the countercurrent washing principle and fully continuous or cycle-dependent batch washing machines. However, further savings of detergent, water, particularly rinsing water, energy and time have been prevented by the absence of reliable, continuous and automatic processes for determining the concentration of detergents and bleaches in the liquor. The measuring signal of such processes could be used to control metering, to terminate individual process steps, etc., so that a satisfactory washing result could be obtained with the minimum use of energy, detergent, water and time. A determination process of the type in question would enable optimal time-related concentration profiles of detergents and bleaches to be maintained in batch washing machines. Optimization of the rinse cycle with a minimum quantity of water in a short time would also be possible without an excessive proportion of the wash liquor remaining behind in the washed fabrics.
Although processes for determining the concentration of detergents and bleaches are known, they are attended by a number of disadvantages which have prevented them from being used on a wide scale in practice. They are generally based on the measurement of physicochemical parameters, for example conductivity and pH value. However, conductivity and pH measurements can be affected by the widely fluctuating introduction of electrolytes and acids or bases with the soiled washing.
It is also known that the concentration of chemical substances in a liquid can be determined by flow injection analysis. In this process, a reagent is added to the liquor in a diluted or undiluted sidestream and the concentration is photometrically determined.
Where flow injection analysis is used to determine the concentration of detergents or bleaches in the wash liquor, other substances which must be ecologically and toxicologically safe often have to be added to the detergent. However, in order to determine the concentration with sufficient accuracy, relatively large quantities of these substances often have to be added. Additional effort is involved in the addition of the reagent to initiate the color reaction. The measuring solutions have to be separately disposed of. The general need for a reduction in the level of manual intervention in the washing process conflicts with the need to replace the spent reagents. Other problems are caused by the cloudiness and suspended particles present in the solution to be measured. In order to avoid interference with the extinction measurement, the particles in question have to be removed beforehand, for example by filtration. Since flow injection analysis cannot take place in the wash liquid itself, an often considerable delay between sampling and measurement has to be accepted.
DE 29 49 254 A1 describes a washing process in which the concentration of a detergent is determined from its fluorescence radiation. However, where several detergents are used in the same wash liquor, their concentrations cannot be individually determined.
Accordingly, the problem addressed by the present invention was to provide a process of the type mentioned at the beginning which would not have any of the disadvantages mentioned above.